This invention relates to a coaxial engine starter and, more particularly, to a coaxial engine starter for a vehicular engine.
The conventional vehicular engine starter is constructed as illustrated in FIG. 1. The conventional engine starter 1 shown in FIG. 1 comprises a d.c. motor 2, an over-running clutch 4 slidably fitted over an output rotary shaft 3, a planetary speed reduction gear 5 for reducing the rotational force of the armature rotary shaft 2a of the d.c. motor 2 to transmit it to the clutch outer member 4a of the over-running clutch 4 through the output rotary shaft 3, and a shift lever 8 for sliding the over-running clutch 4 along the output rotary shaft 3, the shift lever 8 engaging at its one end with the plunger rod of a solenoid switch 6 mounted on a side of the d.c. motor 2 and being connected at its the other end to an annular member 7 mounted to the over-running clutch 4.
However, in the conventional engine starter as shown in FIG. 1, the solenoid switch 6 for moving the shift lever 8 and for closing electrical contacts connecting an electrical source to the d.c. motor 2 is positioned on one side of the d.c. motor 2 in a parallel, side-by-side relationship and the shift lever 8 must be provided for slidably moving the over-running clutch 4 along the output rotary shaft 3 into engagement with the engine ring gear. Therefore, with the conventional starter, the engine layout in the engine compartment of a vehicle is restricted due to the structure and the configuration of the starter.
In order to eliminate the above disadvantages, a coaxial engine starter 10 as shown in FIG. 2 has been proposed, in which the solenoid switch is coaxially positioned at one axial end of the d.c. motor so that the overall starter configuration may become a simple elongated cylinder. According to the coaxial engine starter 10 of this proposition, a d.c. electric motor 11 has a hollow armature rotary shaft 12 and a plunger rod 13a of a solenoid switch 13 positioned at the rear end of the d.c. motor 11 is inserted into an inner passage 12a of the armature rotary shaft 12 so that the inserted front end of the plunger rod 13a abuts against the rear end of an output rotary shaft 14 coaxially disposed at the front end of the armature rotary shaft 12 and inserted into the inner passage 12a of the armature rotary shaft 12, whereby the output rotary shaft 14 can be pushed forward.
It is seen that a sun gear 15a is formed on the outer circumference of the front end of the armature rotary shaft 12 and a plurality of planetary gears 15b are in mesh with the sun gear 15a. These planetary gears 15a also mesh with an inner gear 15c formed in the inner circumferential surface of the frame 16 and are rotatably supported by shafts 15d secured on a carrier 15e. The sun gear 15a, the planetary gears 15b, the inner gear 15c, the shafts 15d and the carrier 15e together constitute a planetary speed reduction gear 15 which reduces the rotational speed of the armature rotary shaft 12. On the output rotary shaft 14, an over-running clutch 17 is fitted, of which clutch inner member 17a is engaged with the output rotary shaft 14 by helical splines 14b of spline formation portion 14a having an outer diameter larger than the inner diameter of the inner passage 12a of the armature rotary shaft 12, so that the output rotary shaft 14 is allowed to axially slide while being rotated by the clutch inner member 17a. On the front end of the output rotary shaft 14, a pinion 18 which engages and disengages relative to the engine ring gear (not shown). When the output rotary shaft 14 is moved forward, the pinion 18 meshes the engine ring gear to rotate the engine.
However, since it is very difficult to precisely axially align the planetary speed reduction gear 15 and the armature rotary shaft 12, they are often misaligned or brought into a non-coaxial relationship which brings about a very unstable condition. Therefore, the planetary gears 15b can be destroyed or the planetary speed reduction gear 15 can make a noise during a high speed rotation or when a large impact is applied. Particular in the case of a coaxial starter, since the shafts 15d for rotatably supporting the planetary gears 5b are secured to the carrier integrally formed in the clutch outer member 17b of the over-running clutch 17, the clutch outer member 17b can also be misaligned, resulting in the formation of hit marks on cum surfaces of the over-running clutch 17.
Further, in order to provide a stop for limiting the rearward movement of the output rotary shaft 14 beyond a certain point, the front end of the armature rotary shaft 12 is defined so that it abuts the rear end surface of the spline formation portion 14a of the output rotary shaft 14. However, since there is a relative rotation between the armature rotary shaft 12 and the output rotary shaft 14, the engaging surfaces are very quickly worn, posing a problem that an accurate stop position of the output rotary shaft is difficult to maintain.